The present invention relates to a piezoelectric thin-film device for use in ink-jet recording apparatus or the like, a process for its manufacture, and an ink-jet recording head using such piezoelectric thin-film device.
Piezoelectric thin films typically made of lead zirconate-titanate (hereinafter sometimes abbreviated as PZT) are formed by various methods including a physical vapor deposition (PVD) technique such as sputtering, a chemical vapor deposition (CVD) technique and spin coating such as a sol-gel method, followed by a heat treatment at a high temperature of 700 to 1000.degree. C. A problem with such piezoelectric thin films is that they cannot be made thicker than 1 .mu.m. To solve this limitation and form thicker piezoelectric films, two approaches are conventionally taken, i.e., increasing the film deposition time or repeating the film formation several times.
Another approach for increasing the thickness of piezoelectric thin films is under review and is based on the use of hydrothermal synthesis which permits the intended reaction to proceed in a low-temperature (.ltoreq.200.degree. C.) environment. According to a recent article entitled "Preparation of PZT crystalline films by hydrothermal synthesis and their electrical characteristics" in the preprint for the lectures to be read at the 15th Workshop on Electronic Materials, Japan Institute of Ceramics, the hydrothermal synthesis technique as a method for increasing the thickness of piezoelectric thin films comprises a seed crystal forming process in which PZT seed crystals are precipitated on the surface of a metallic titanium substrate and a crystal growing process in which PZT crystals are precipitated and grown on the PZT seed crystals.
The conventional approaches for manufacturing piezoelectric thin films by sputtering, the sol-gel method or the like require a subsequent heat treatment at such high temperatures that they are not suitable for producing films thicker than 1 .mu.m unless a considerably prolonged time is spent for film formation. Also cracks will develop even if a film of desired thickness is formed.
Thick films can be formed at low temperatures by the hydrothermal synthesis technique but, on the other hand, the crystal grains produced will be as large as several micrometers so that neither dense, smooth films are formed nor is it possible to achieve fine patterning. In order for piezoelectric thin films to be used as piezoelectric devices in an ink-jet recording apparatus and the like, the films must be as thick as about 1 to 10 .mu.m.